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CC - Drainage Calc's PROJECT NO . 10= 17=027 DRAINAGE CALCULATIONS FOR Little Creek No . 1 City of Meridian Ada County , Idaho April 26 , 2017 NAL � 2449 17 10 \off J�V CJEUEB J • UmB ENGINEERS , INC . 250 S . Beechwood Drive , #201 Boise , Idaho 83709 208=376 =7330 PROJECT NO.10-17-027 Little Creek No. 1 SITE OVERVIEW Little Creek No. 1 Subdivision is located at the southwest corner of Wilson Lane and N. Locust Grove Road in Meridian, Idaho.The proposed development consists of 24 townhome buildings and a clubhouse on approximately 8.2 acres. EXISTING DRAINAGE The existing project site presently consists of a vacant agricultural field. The site is bounded by developed single family residential properties to the east,commercial development to the north and agricultural land to the west and south.The ground slopes gently from southwest to northeast at grades generally less than 2%. DRAINAGE DESIGN CONCEPT The proposed stormwater improvements include the installation of roadways, pipe networks, stormwater treatment systems,and storage facilities.The surface flow will be directed to and contained within the road sections to designed low points where inlets will capture the stormwater and convey it through a pipe network to a discharge location. A treatment system will be installed for each pipe network prior to allowing the stormwater to be be discharged to the storage facility. The site was divided into catchment areas based on the inlet locations. Each catchement area was analyzed for the 25-year flow rate for conveyance,the water quality event for treatment and the 100-year runoff for storage. CALCULATION METHODS Calcualtions were prepared in accordance with the current edition of the Ada County Highway District Stormwater Policy Manual using the rational method(Q=CIA).The catchment areas are shown on the Drainage Catchment Plan. The average rainfall intensity is estimated from the "Rainfall Intensity-Duration-Frequency Relationship"figure for each storm event noted. The time of concentration is determined using the TR-55 method and combines the longest overland grass flow time to gutter flow time. Calculations and spreadsheets are included with this report for all catchment areas. SOIL CONDITIONS Based upon the preliminary soils and subsurface investigation provided in the soils report for this subdivision,the existing soils will accept the runoff. However,in the event that during construction the contractor encounters either groundwater or rock,a revised design will be done based upon field conditions. F:\Projects\JUB\10-17-027 Little Creek Phase 1\Drainage\10_17_027_DrainageCalcs_Add Access Road.xlsx N 0 _ oZ O O M N m M N m l0 co Ott to 00 C?) co n co N m C) 7 m U m a W J O U! (h Cl m com a) n n CM M m OD C) O O ?� V V V a r r M M CO co V' a cV N 00 ¢a Q o 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 m a) ¢ $ 0 o w CO) :° rn ro F N OV N O N 0 E > O ¢ m `o +S+ C C m o E o E co o vn N n rmi o 0 0 (D O L N () O O O O O O O 66 (a O) (n - (D Q = E a T fn 7 — O T O O O C Or LO _ rt+ > > U - N Q (D « • n fC OC % G) ¢ 0 LO n N uI p .@ O CL C Ic C u0~i cf LO to M uI m M C7 cL m m > N xx . O m Q (D .() C O O O a c6 oz O M ,n ¢ co m m n co m C) O MU0 N o d v co M v N o 0 10 13 II 11 O O N O O O O O o O O 0 0 C1 > > U .a .N . N f3 fC N N N N (D (D n n n n N N M M 0 0 oU) u) N m lD m O aq* CO M m lD O O O O Q O O O 0 0 L N m m (D (D n n (n LO m co (D o Nt v 0 0 Cl) o o v a O O m 0) n n 0 0 C3 00 00 00 00 c r r r r r r r r O O O N N CIJ (O (D f� n 0 0 (,0 (D (D N N um itl C Q D (D (o to (\j N (o co n u) (o (D v a 03 0 0 0 0 0 0 0 0 0 0 0 0 o c m T 32 U (D m m m m m m m (L T ¢ > o c LO In N C C, N N N N N (m Q [0 C C N 7 (1) O U a- cr. C N � W � N W N W Lo lC LO O) (n l0 II /IIy II II II N m m m m CO m m 0 0 U — ¢ ~ � F r F � H � � F G) m m m m m m N L (G (D (D (O (D m m e C O O O O O O C)LO u) (D (n LO LO u) O O V m m m m 0! rn m m u) y O O ClO C) C) O O O x a N 0 Q N E s m U O Cn 3 0 ¢ 3 O J aD (� N c m (D (O m m N co Co 0 N M m co m V' O O O .-. LL co E r o ai ui o 0CD tl rn m O 0 0 m m S. t O O N O M C( c m J G) _ _ - Q G J ¢ 0 O II J N N TO CD _ _ O C) r ( � Cn � imm G C:) 'ou) LO (O (O (O to u7 O O c E r 0 0 m O � m (D (0 O O 00 O = O NO N M © O ,C D_ O O O O = O O _ ro o a N O J ° °c 5 a 0 CD0 m a+ U L - C/j y m t m U l9 O r N a m v M m 7 O c O � N 'c o N > U O d N O T W m m (D .c (V p) .�. o O o 0 o O o o \ N CO) O > v ui 0 v m n n m m m o 0 4 O N c O ( N LL O J O O ¢ N 0 II C J d :n ¢ M co m co co co M 7 «•Cl) _ m o) rn rn m m m m m O O Co O O O O (' >i a m O o a LL N i M OL Cl ¢ m U w L C7 aE) E Q Fa) F Basin A PROJECT NO. 10-17-027 Little Creek No. 1 Contributing Catchment Areas : A Required Water Quality Volume : 829 ft' Required Water Quality Flow Rate: 0.41 cfs Required Storage Volume : 2,036 ft' Seepage Bed Th( Volume Calculations Storage Duration Depth = 4 . 5 it Length = 190 ft Infiltration Area = 11140 ft2 Width = 6 ft Infiltration Rate = 8 in ./hr ## Void Ratio = 40 % Trench Infiltration = 760 ft3/hr Trench Volume = 2,052 ft3 Time for 90% Percolation = 0.98 hr Sand and Grease Trap Calculations Box Volume = 1000 gallon Interior Box Width = 48 in QWa = 0 .41 ft /sec Baffle Baffle Separation = 20 in Throat Velocity = 0.06 ft/sec Number of Boxes = 1 Throat Area = 6 .67 ft' Throat Velocity must be < 0 . 50 ft/sec F:\Projects\JUB\10- 17-027 Little Creek Phase 1 \Drainage\10_17_027_DrainageCalcs_Add Access Road.)dsx Page 4 of 11 Basin B PROJECT NO. 10-17-027 Little Creek No, 1 Contributing Catchment Areas : B Required Water Quality Volume : 883 ft' Required Water Quality Flow Rate : 0.43 cfs Required Storage Volume : 2, 167 ft' Seepage Bed Th Volume Calculations Storage Duration Depth = 6 ft Length = 76 ft Infiltration Area = 912 fe Width = 12 ft Infiltration Rate = 8 in ./hr ## Void Ratio = 40 % Trench Infiltration = 608 ft3/hr Trench Volume = 2, 189 ft3 Time for 90% Percolation = 1 .31 hr Sand and Grease Trap Calculations Box Volume = 1000 gallon Interior Box Width = 48 in QWQ = 0 .43 ft3/sec Baffle Separation = 20 in Throat Velocity = 0. 06 ft/sec Number of Boxes = 1 Throat Area = 6 . 67 ft2 Throat Velocity must be < 0 . 50 ft/sec F:\Projects\JUB\10-17-027 Little Creek Phase 1 \Drainage\10_17_027_DrainageCalcs_Add Access Road.xlsx Page 5 of 11 Basin C PROJECT NO. 10.17-027 Little Creek No. 1 Contributing Catchment Areas: D Required Water Quality Volume: 361 ft' Required Water Quality Flow Rate: 0. 18 cfs Required Storage Volume: 886 ft' Seepage Bed Th Volume Calculations Storage Duration Depth = 6 ft Length = 37 ft Infiltration Area = 370 ft Width = 10 ft Infiltration Rate = 8 in ./hr ## Void Ratio = 40 % Trench Infiltration = 247 ft3/hr Trench Volume = 888 ft, Time for 90% Percolation = 1 .32 hr Sand and Grease Trap Calculations Box Volume = 1000 gallon Interior Box Width = 48 in Qwa = 0 . 18 ft3/sec Baffle Separation = 20 in Throat Velocity = 0.03 ft/sec Number of Boxes = 1 Throat Area = 6 . 67 ft2 Throat Velocity must be < 0 . 50 ft/sec F:\Projects\JUB\10-17.027 Little Creek Phase 1 \Drainage\1 Oil 7_027_DrainageCalcs_Add Access Road .xlsx Page 6 of 11 Basin D PROJECT NO. 10-17-027 Little Creek No, 1 Contributing Catchment Areas : D Required Water Quality Volume : 802 ft' Required Water Quality Flow Rate : 0.39 cfs Required Storage Volume : 1 ,970 ft' Seepage Bed Th Volume Calculations Storage Duration Depth = 6 ft Length = 69 ft Infiltration Area = 828 ft Width = 12 ft Infiltration Rate = 8 in ./hr ## Void Ratio = 40 % Trench Infiltration = 552 ft3/hr Trench Volume = 1 ,987 ft3 Time for 90% Percolation = 1 .31 hr Sand and Grease Trap Calculations Box Volume = 1000 gallon 3 Interior Box Width = 48 in QwQ = 0 • 39 ft /sec Baffle Separation = 20 in Throat Velocity = 0.06 ft/sec Number of Boxes = 1 Throat Area = 6. 67 ft2 Throat Velocity must be < 0 . 50 ft/sec F:\Projects\JUB\10-17-027 Little Creek Phase 1 \Drainage\10_17_027_Drainagecalcs_Add Access Road.xlsx Page 7 of 11 Basin E PROJECT NO. 1 Owl 7-027 Little Creek No, 1 Contributing Catchment Areas: E Required Water Quality Volume : 749 ft' Required Water Quality Flow Rate : 0.37 cfs Required Storage Volume : 1 , 839 ft' Seepage Bed wiwi Th Volume Calculations Storage Duration Depth = 6 ft Length = 96 ft Infiltration Area = 768 ft Width = 8 ft Infiltration Rate = 8 in ./hr ## Void Ratio = 40 % Trench Infiltration = 512 ft3/hr Trench Volume = 11843 ft3 Time for 90% Percolation = 1 .32 hr Sand and Grease Trap Calculations Box Volume = 1000 gallon Interior Box Width = 48 in QWo = 0 .37 ft3/sec Baffle Separation = 20 in Throat Velocity = 0.06 ft/sec Number of Boxes = 1 Throat Area = 6 . 67 ft' Throat Velocity must be < 0 . 50 ft/sec F:\Projects\JUB\10.17-027 Little Creek Phase 1 \Drainage\10_17_027_DrainageCalcs_Add Access Road.xlsx Page 8 of 11 Basin F PROJECT NO. 10-17-027 Little Creek No, 1 Contributing Catchment Areas: G Required Water Quality Volume : 883 ft' Required Water Quality Flow Rate: 0.43 cfs Required Storage Volume : 2, 167 ft' Seepage Bed ThE Volume Calculations Storage Duration Depth = 6 ft Length = 70 ft Infiltration Area = 910 ft Width = 13 ft Infiltration Rate = 8 in ./hr ## Void Ratio = 40 % Trench Infiltration = 607 ft3/hr Trench Volume = 21184 ft3 Time for 90% Percolation = 1 .31 hr Sand and Grease Trap Calculations Box Volume = 1000 gallon Interior Box Width = 48 in QWQ = 0 .43 ft /sec Baffle Baffle Separation = 20 in Throat Velocity = 0.06 ft/sec Number of Boxes = 1 Throat Area = 6 . 67 ft2 Throat Velocity must be < 0. 50 ft/sec FAProjecis\JU13\10-17-027 Little Creek Phase 1 \Drainage\10_17_027_DrainageCalcs_Add Access Road.xlsx Page 9 of 11 Basin G PROJECT NO. 10-17-027 Little Creek No. 1 Contributing Catchment Areas: G Required Water Quality Volume: 562 ft' Required Water Quality Flow Rate: 0.28 cfs Required Storage Volume: 1 ,586 ft' Seepage Bed Th Volume Calculations Storage Duration Depth = 4 . 5 it Length = 74 ft Infiltration Area = 888 ft2 Width = 12 ft Infiltration Rate = 8 in ./hr ## Void Ratio = 40 % Trench Infiltration = 592 ft3/hr Trench Volume = 11598 ft3 Time for 90% Percolation = 0.85 hr Sand and Grease Trap Calculations Box Volume = 1000 gallon Interior Box Width = 48 in QWQ = 0 . 28 ft'/sec Baffle Separation = 20 in Throat Velocity = 0.04 ft/sec Number of Boxes = 1 Throat Area = 6. 67 ft2 Throat Velocity must be < 0 . 50 ft/sec FVrojects\JU13\10-17-027 Little Creek Phase 1 \Drainage\10_17_027_DrainageCalcs_Add Access Road.xlsx Page 10 of 11 Boise Area Intensity- Duration- Frequency Intensity ( inches per hour) Design Storm 2 5 10 25 50 100 Tc 0 . 17 10 min 0 . 69 1 . 15 1 .45 1 . 85 2 . 20 2 . 58 0 . 25 15 min 0 . 59 0 . 97 1 . 22 1956 1 . 86 2 . 18 0 . 33 20 min 0 . 49 0 . 81 1 . 01 1 . 30 1 . 54 1 . 81 0 . 42 25 min 0 . 43 0 . 71 0 . 89 1 . 14 1 . 35 1 . 58 0 . 50 30 min 0 .41 0 . 67 0 . 85 1 . 08 1 . 29 1 . 51 0 . 58 35 min 0 . 34 0 . 56 0 . 70 0 . 90 1 . 07 1 . 25 0 . 67 40 min 0 . 31 0 . 51 0 . 64 0 . 82 0 . 98 1 . 15 0 . 75 45 min 0 . 29 0 .48 0 . 60 0 . 77 0 . 91 1 . 07 0 . 83 50 min 0 . 27 0 . 45 0 . 56 0 . 72 0 . 85 1 . 00 0 . 92 55 min 0 . 26 0 . 43 0 . 54 0 . 69 0 . 82 0 . 96 1 . 00 1 hour 0 . 26 0 . 43 0 . 54 0 . 69 0 . 82 0 . 96 2 . 00 2 hours 0 . 16 0 . 25 0 . 31 0 . 39 0 . 46 0 . 54 3 . 00 3 hours 0 . 13 0 . 19 0 . 23 0 . 29 0 . 34 0 . 40 6 . 00 6 hours 0 . 09 0 . 12 0 . 14 0 . 18 0 . 21 0 . 25 12 . 00 12 hours 0 . 06 0 . 08 0 . 10 0 . 12 0 . 14 0 . 16 24 . 00 24 hours 0 . 04 0 . 06 0 . 06 0 . 08 0 . 09 0 . 10 NOAA Atlas 2 Intensity Duration Frequency 3 . 5 -- 2 year 3 -X- 5 year . . 2 . 5 -X- 10 year L 2 x -� 25 year V \ ---�- 50 year 1 . 5 �x 100 year rM 005 0 10 min 15 min 30 min 1 hour 2 hours 3 hours 6 hours 12 hours 24 hours Duration in minutes and hours i I I i 0 AV I I I I I I BASIN G 0.42 ACRES I I , I I I I i I I I I ; I I a I � ( I I I I I � I I I I I ( I I I I I I i \ 0 e g k 9 yw 3 r rl U d 9 0 50 100 cW oa SCALE IN FEET a� R LITTLE CREEK SUBDIVISION PHASE 1 I i--- Meridian, Idaho orj*13 -A DRAINAGE CATCHMENT PLAN 6 0 J-U-B ENGINEERS,INC.